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Building Regulations or Planning Permission?

Many thanks to Nigel Hockin of GBS Joinery for researching and writing this document. Note: the regulations may have changed since this was written in 2008.

Building regulations

The installation of replacement windows and doors (doors with a glazed area of 50% or more) requires building regulation certification.

The building regulations pertaining to the replacement of windows and doors are as follows

  • Document 'L' conservation of fuel
  • Document 'N' protection against impact
  • Document 'B' fire escape
  • Document 'F' ventilation
  • Document 'C' resistance to moisture

Document 'L'

As part of the governments strategy to reduce energy use and CO2 emissions building regulations approved document 'L', effective from 1st April 2002 revised April 2006 requires all replacement windows and doors with more than 50 % glazed area to conform to a specific energy value or 'U' value of ; 2.0 W/m2 0K, ( watts per square metre, per degree Kelvin ) .

All replacement windows and doors must comply with document 'L' and achieve the required 'U' value by the use of double glazed units with the correct air gap combined with either low emissive coated glass in the form of Pilkington 'K' glass or Argon gas filled.

Document 'N'

Calls for safety glass to all critical areas conforming to BS 6206 requiring the glass if broken to disintegrate into small particles or to not to break into pointed shards, also the safe opening and closing of windows.

Document 'B'

Calls for emergency egress through windows in habitable rooms, no egress is required via windows to rooms on a second floor 4.5 meters from ground level.

The opening part of an egress window must not exceed 1100 mm from floor level.

When replacing a sash window where the lower sash opens its replacement must also open at the same point therefore a so called mock sash window where the lower sash is fixed and the top sash hinges outward may not be used.

The minimum square area of clear unobstructed opening in an egress window must be at least 0.33 m2, the minimum dimensions being 450mm high by 450mm wide but please note that these dimensions cannot be used together as the square area is only 0.20 m2.

Document 'F'

Calls for adequate ventilation and is required to combat condensation and mould growth , this is not easily defined as to not compromise document 'L'.

Trickle vents may be fitted but these are an ugly addition to a historic building, vent stops may be used to hold the window in open position without compromising security and safety, wall vents may be fitted in particularly where gas fires are fitted, mechanical ventilation bathrooms and kitchens will meet the ventilation requirements of these rooms.

Document 'C'

Requires the joint between walls and window / door frames to resist the penetration of precipitation and moisture this can be achieved by the use of pvc DPC (damp proof course), sealants and expanding foam.


Where windows and doors are replaced like for like planning permission is not required unless the appearance of the property or the window apertures are altered or the property lies within a conservation area a National Park or is a listed building, in which case LBC (Listed Building Consent) will be required.

Historic Buildings

The building regulations recognise the need to conserve the characteristics of historic buildings where practically possible without compromising the integrity of the property therefore a sympathetic approach is required when considering works to a listed buildings, buildings within a national park or a conservation area, and in these cases it would be advisable to seek the opinion of the local conservation officer before any work is carried.


The installation of replacement windows requires certification, certification that will be required by future prospective purchasers of the property, their surveyors, solicitors and lenders and now Hip's (home information pack).

Installers who are members of the following all meet the vetting criteria of self certificating schemes known as FENSA or CERTASS:

  • The Glass & Glazing Federation
  • The British Woodworking Federation
  • The Guild of Master Craftsmen

Please note that there is no requirement or obligation to participate in any such scheme.

Alternatively certification can be sought from your local authority Building Control or by an RICS (Royal Institute of Chartered Surveyors) or CIOB (Chartered Institute of Building) approved inspectors.

Windows supplied for new build or extensions to property where the project is already covered by a building regulation notice require no further inspection or certification.

The replacement of casements or sashes or doors within retained original main frames may not require certification.

Please be aware that the responsibility to meet the building regulations and local authority planning requirements lies with the property owner.

Non-compliance with the building regulations or planning requirements will be in direct breach of the Building Act 1984 and or Building Regulations 2000 and the Town and Country planning act 1990 and may result in enforcement.


The renovation or total replacement of windows to a listed building is classed by HM Revenue & Customs as repair and maintenance and is therefore subject to VAT at the current standard rate.

Where LBC has been applied for and granted and the installation is carried out by a VAT registered company VAT may be charged at 0%

Clients are free to contact their local HM Revenue & Customs Adjudication for a judgment of individual cases, a decision will take 14 days.


Approved documents are intended to provide guidance and assist compliance with the building regulations, however there may be alternative methods adopted that achieve compliance.

This information is freely given in good faith and is based upon the writer's years of experience, interpretation and understanding of the building regulations which are not practically defined therein therefore no liability can be accepted for their interpretation.

Be aware that the regulations may have changed since this was written in 2008.

Nigel Hockin   GBS Joinery
April 2008

© 2022 Nick Iredale